EP0128633B1

EP0128633B1 - Method of measuring color difference between a sample and a standard dyestuff

Info

Publication number: EP0128633B1
Application number: EP84300817A
Authority: EP
Inventors: Masakazu Suzuka; Hiromu Ohashi; Yukio Murata; Nobuyoshi Fujitsuka
Original assignee: Sumitomo Chemical Co Ltd
Current assignee: Sumitomo Chemical Co Ltd
Priority date: 1983-06-14
Filing date: 1984-02-09
Publication date: 1990-04-25
Anticipated expiration: 2004-02-09
Also published as: EP0128633A2; EP0128633A3; DE3482057D1; KR850000675A; US4613947A; JPS59231428A; JPH0820310B2

Description

This invention relates to a method for measuring the color difference between a sample and a standard dyestuff. More particularly, it relates to a method for measuring color difference which is useful for the quality control of dyestuffs in the dye manufacturing industry.
GB-A-1229307 describes a method of determining whether or not the color of a mixture of colorants falls within prescribed tolerance limits for color deviation from a standard color. The method involves determination (by experimentation or calculation) of deviations in reflectance or transmittance values, in spectral regions of maximum absorbance for each respective colorant. This determination is carried out for various mixtures of the colorants to provide a diagram in which the prescribed tolerance limits are represented. The deviation, from the standard, of a sample is measured and compared with the diagram. This method does not allow prediction of any color prior to measurement, let alone prediction of the color of a dyed material.
At present in a dye manufacturing works, the quality control is performed by dyeing an appropriate material with freshly manufactured dye and, in parallel, with a reference dye selected as standard, and measuring the quality difference between the dyed materials. For instance, when using equal amounts of a dye selected as a standard for comparison (hereinafter referred to as standard dye) and a dye to be measured for the color difference (hereinafter referred to as sample dye), dyeing is carried out simultaneously, there occurs in most cases a difference in the depth of color between each dyed material depending upon the coloring matter content of each dye. In order to correct the color difference resulting from the difference in the depth of color, the concentration of dye in the bath is adjusted so that the depth of color of the dyeings may be equalized. The color properties of a dye are evaluated based on the color difference between the dyeings obtained by use of the adjusted bath. This color difference is resolvable into a difference in hue such as, for example, inclination to red or inclination to blue, and a difference in so- called brightness which is dependent on the purity of color. The evaluation of a dye by human visual judgement is usually done in terms of three values including the difference in hue, the difference in brightness, and, in addition, the dyeing strength which is the percentage ratio of the quantities of dyes or concentrations of dyebaths necessary for the dyeings of equal hue depth. In the conventional test for color properties of a sample dye in comparison with those of a standard dye, it is a usual practice to carry out a sequence of procedural steps comprising preparation of dye solution, dyeing, washing, and drying for both dyes simultaneously and then compare the dyeings with each other. Since such a method consumes a great deal of time and man-power, there is a rising requirement for a method which is more economical, rapid, and capable of predicting the result of dyeing.
The present inventors, therefore, made an extensive study by using numeral experimental data to answer the above requirement and, as a result, accomplished the present invention.
This invention provides a method for measuring the color difference between a sample dye and a standard dye by testing the color property of both dyes, which comprises the steps of isolating from dyes of the same family each of the coloring matter components having a dyeing affinity and having the possibility of existing in the dye; measuring the spectral absorbance or spectral transmittance of each component in solution form to obtain data 1 to be filed; preparing or selecting two or more dyes having such compositions that the proportions of the coloring matter components are different to some degrees from those of the sample dye, then quantitatively analyzing said prepared or selected dyes and a standard dye for their coloring matter components; calculating the spectral absorbance or spectral transmittance of each of said prepared or selected dyes and said standard dye by the method of color mixing calculation in accordance with the composition of each dye using the results of above quantitative anaylsis and the filed data of spectral absorbance or spectral transmittance of each coloring matter component; calculating the color difference in solution between each of said prepared or selected dyes and the standard dye; dyeing with said prepared or selected dyes and the standard dye to determine the color difference by colorimetry; determining statistically the numerical relationship between the color difference of dye solution and the color difference of dyeings to acquire data 2 (the data 1 and 2 being the base data to be collected in advance for the purpose of using in the subsequent evaluation of color); after collecting the foregoing data 1 and 2, - analyzing quantitatively the sample dye for the coloring matter components; calculating the tristimulus values of the solution of sample dye from the results of said quantitative analysis and the spectral absorbance or spectral transmittance of each coloring matter component (data 1); calculating the color difference in solution from the calculated tristimulus values and the tristimulus values of the standard dye (which are determined previously or simultaneously); and converting the calculated color difference of solution into the color difference of dyeings by means of the determined relationship between the color difference of solution and the color difference of dyeings (data 2).
More particularly, this invention provides a method for measuring the color difference between a sample dye and a standard dye by testing the color properties of both dyes, which comprises determining, optionally in advance, the relation of the color difference of dyeings (between the standard dye and the dyes of the same family) to the color difference of dye solutions (between a standard dye and the dyes of the same family) by the steps described below using the standard dye and two or more, preferably several, representative samples, then calculating the color difference of dye solution between the standard dye and a sample dye, and predicting the color difference between a dyeing of the sample dye and a dyeing of the standard dye from the calculated color difference between the respective sample and standard dye solutions by referring to the relation obtained above.
Such a method comprises the following steps:

(1) Each of the components contained in the dyes of the same family is separated and collected separately by chromatography. For each separated component the spectral absorbance curve is derived from measured values and from each curve a spectral absorbance curve per unit of each component is derived. At this stage, any correction may be made by the use of a weighting factor pertaining to the dyeing affinity or the like.
(2-1) The calculation for color mixing is performed by using the absorbance curve per unit of each component obtained in (1) and the results of quantitative analysis of the separated components with respect to the standard dye and representative samples of the same family as that of the standard dye. The correction by the weighting factor may be made at this stage unless it has been made in (1).
A color coordinate system representing a value of color property unaffected by the variation in concentration of the solution, such as values of complementary chromaticity coordinates is selected. Complementary tristimulus values QX, QY, QZ are calculated for the standard dye and the sample dye by the same method of calculating the tristimulus values using the absorbance in place of the transmittance. From the calculated complementary tristimulus values, there are obtained complementary chromaticity coordinates xQ, yQ and the integrated optical density SQ, which is the sum of QX, QY, QZ.
(2-2) A dye (which can be the standard dye) is selected from the dyes of the same family and tristimulus value X, Y and Z are calculated from the spectral transmittance curve of the dye. These values are then transformed into a suitable uniform color scale. In the coordinate diagram of this color system, four sets of tristimulus values given by chromaticity points each representing a respective change, from a given chromaticity point of the dye of one unit independently in hue difference and in saturation or brightness difference are calculated and the corresponding transmittance curve is derived by a color mixing calculation. The transmittance curve is transformed into the absorbance distribution curve to obtain the complementary chromaticity coordinates of each chromaticity point. From the difference between these coordinates and the complementary chromaticity coordinates of the dye selected above, the relation of the hue difference and saturation or brightness difference to the difference in complementary chromaticity coordinates in the uniform color scale is established.

By referring to the relationship established above, the color difference-of solution of the representative sample relative to the standard dye is calculated in terms of hue difference and saturation difference or brightness difference.
The above operation is repeated on two or more, preferably several, representative dyes each different from one another in their proportions of coloring matter components.

(3) Dyeings are prepared from the standard dye and the representative samples of which the color difference of solution have been determined above. From the dyeings, there is obtained the color difference (in terms of hue difference and saturation or brightness difference) of the representative dye relative to the standard dye.
(4) The relationship between the color differences (between respective representative dyes and the standard dye) of dye solutions determined in (2) and the color differences (between respective representative dyes and the standard dye) of dyeings determined in (3) is found in terms of hue difference and saturation or brightness difference.
(5) Using the standard dye and the sample dye, the color difference of solution of the sample dye relative to the standard dye is calculated in terms of hue difference and saturation of brightness difference, as described in (2).
(6) The color difference of dyeings of the sample dye as compared with the standard dye is predicted from the color difference of a solution of the sample dye as compared with the standard dye obtained in (5) and the relationship established in (4).

According to the present invention, it becomes possible to predict the color difference of dyeings from the results of quantitative analysis for dye components without needing the complicated dyeing test. The advantages of the present method may be summarized as follows:

(a) The exclusion of a series of procedures for the dyeing test results in speed-up and simplification of operation steps and savings in man-power and energy.
(b) The conventional method for the evaluation of color difference by the dyeing test includes a number of factors which tend to decrease precision of the evaluation, such as differences in the type and shape of the material to be dyed, variation in the evaluation results caused by the variation in dyeing procedure and dyeing equipment, visual judgement susceptible to differences among observers, etc., whereas the precision is much improved in the present invention by the preclusion of such factors.
(c) Since the color difference of the sample dye as compared with the standard dye is found precisely and speedily, the method is applicable to process control in dye manufacture with accompanying pronounced economic advantages such as reduction of defective products, curtailment of the waiting time, etc.
(d) The present method can be widely utilized in the development stage of novel dyestuffs, resulting in speed-up of the research work.
(e) Requirement from the user of a dye for a change in hue can be quickly answered.

A brief description of the accompanying drawings is given below.

Fig. 1 is a ftow chart of the entire procedural steps of a method embodying the present invention. In Figs. 1 and 2, the encircled figure corresponds to the step number described above.
Fig. 2 is a flow chart or the measurement of color difference between that of a given dye solution and that of a standard dye solution. Step (1) is a step to find color properties (in solution) of the components constituting a dye. Step (2) is a step to find directly the absorbance distribution curve by the color mixing of the components constituting a dye and to find the color difference of a dye solution as compared with a standard dye solution from the relationships between the hue difference as well as brightness difference and the complementary chromaticity coordinates.
Figs. 3 to 11 are graphs pertaining to C.I. Disperse Blue 301 and Fig. 13 is a graph pertaining to C.I. Disperse Blue 79.
Fig. 3 is a liquid chromatograph.
Fig. 4 and 13 are complementary chromaticity diagrams, wherein 1 refers to the standard dye and 2 to the representative sample.
Fig. 5 is a chromaticity diagram according to CIE 1976 L^*a^*b^* color system. In Fig. 5, 0 is a point on the chromaticity diagram of the standard dye and 1, 2, 3 and 4 are chromaticity points when the chromaticity point 0 undergoes independently a change of one unit.
Figs. 6 to 9 are spectral transmittance curves corresponding to the chromaticity points shown in Fig. 5, wherein 0, 1, 2, 3 and 4 correspond to chromaticity points in Fig. 5, respectively.
Fig. 10 represents interrelationships of the differences in complementary chromaticity coordinates derived from Figs. 6-9, wehrein 0 refers to the standard dye; 1,2,3 and 4 are complementary chromaticity coordinates corresponding to one unit of color difference in solution; and x is complementary chromaticity coordinates of the representative sample.
Fig. 11 represents the relation between the color difference of dyeings and the color difference of dye solution, each as compared with the color of a standard dye.
Fig. 12 is a drawing illustrating the construction of the absorbance measuring system using a spectrophotometer of the rapid scanning type.

As chromatographs used in the present method, mention may be made of column chromatograph, paper chromatograph, and liquid chromatograph. Of these, a high speed liquid chromatograph is especially advantageous. The adjustment of measurements by weighting with respect to dyeing affinity and other factors may be made in step (1) or (2-1).
A typical procedure for carrying out a method embodying the present invention in which liquid chromatography is used as a means of separation is described below in further detail with reference to the drawings.

(1) Each of the components contained in the dye of the same family is separated and collected by high speed liquid chromatography; each separated component is measured to enable a curve representing the distribution of absorbance to be plotted, and from this curve an absorbance distribution curve in the form of a color property per unit quantity of each separated component is derived.
(2) Next, the calculation for color mixing is performed according toone or other of the following sets [1] or [2] of equations, using the absorbance per unit of content and a correction factor for the dyeing affinity (hereinafter referred to as dyeing coefficient) of each separated component with respect to the standard dye and a representative sample. The calculation is carried out by means of a computer.
wherein st and sp refer to standard dye and representative sample, respectively, n is the number of separated individual components, pn is a value obtained by dividing the individual component content by the main component content and multiplying by 100 (hereinafter referred to as ratio of individual component to main component), each content being obtained by the method of peak area normalization, Dnλ is a value obtained by dividing the absorbance of separated individual component by pn, λ being 200-800 nm, and Sn is the dyeing coefficient of an individual component.
wherein n is the number of separated individual components, xQ and yO are complementary chromaticity coordinates, and the mark ^* means mixed complementary chromaticity coordinates.

Fig. 3 is an example of a liquid chromatogram showing the separation of components contained in a blue dye. In Table 2 given later, are shown absorbances per unit of content in the visible spectrum range corresponding to individual components contained in the dye. From the results of color mixing the complementary tristimulus values, QX, QY and QZ are calculated by the following general formulae [3].
wherein xλ, yλ, zλ are spectral tristimulus values such as those shown in CIE 1964 supplementary colorimetric system - X, Y, Z color system for 10° visual field or CIE 1931 standard colorimetric system - - X, Y, Z color system for 2° visual field or in other literature; Pλ is the relative spectral energy distribution of a standard illuminant such as a light source widely used in the color evaluation of dyes, (usually D₆₅); λ is wavelength; and dA is the wavelength interval of the spectrum for the integral calculation, usually 10 or 20 nm, the latter interval being used herein.
Using the above results the complementary chromaticity coordinates xQ and yQ are the integrated optical density, SQ, are computed by the following formulae [4].
A complementary chromaticity diagram, as shown in Fig. 4, is obtained by plotting the above results.
The reasons for the choice of complementary chromaticity coordinates are as follows:

(a) Since the absorbance is proportional to concentration, the ratios among QX, QY and QZ remain constant even if the concentration is variable..
(b) The calculation of color mixing can be done additively on the chromaticity diagram and the trend of color difference becomes easier to understand.

The absorbance distribution curve of one of the dyes in the same family, such as, for example, the standard dye, is transformed by the following formula [5] to the transmittance curve and tristimulus values X, Y and Z are calculated according to the following formulae [6].

The tristimulus values X, Y and Z are then transformed by use of the formula [7] to CIE 1976 L*a*b* colorimetric system.
When the standard luminant is D₆₅ and the vision field is 10°, x_o, y_o and z_o become as follows:
In the a^*b^* chromaticity coordinates diagram of the colorimetric system shown in Fig. 5, four chromaticity-points, [a^*(1), b^*(1)] ... [a^*(4), b^*(4)], are given when the chromaticity point [a^*(0), b^*(0)] representing a hue difference and a saturation or brightness difference undergoes independently a change of one unit. Four sets of tristimulus values [X(1)], Y(1), Z(1)] ... [X(4), Y(4), Z(4)] corresponding to the above four chromaticity points are calculated by the reverse transformation or equations [7]. A spectral transmittance curve Tλ corresponding to each set of tristimulus values is computed by the method of computer color matching calculation or other means (Figs. 6 to 9). These Tλ curves as transformed to the absorbance distribution curves by reverse transformation using equation [5]. The complementary chromaticity coordinates of each chromaticity point are calculated from the formulae [3] and [4]. The relation between these coordinates and the difference between the complementary chromaticity coordinates of the standard dye, [xQ(0), yQ(0)] and the complementary chromaticity coordinates [xQ(1), yQ(1)] ... [xQ(4), yQ(4)] obtained above is determined (Fig. 10).
Based on these relationships shown in Fig. 10, a straight line passing through complementary chromaticity coordinates of the representative sample is drawn in parallel with the straight line passing through the chromaticity points 1, 0 and 2 (hereinafter referred to as constant brightness locus) until it intersects at A the straight line passing through the chromaticity points 3, 0 and 4 (hereinafter referred to as constant hue locus). Another straight line passing through the complementary chromaticity coordinates is drawn in parallel with the constant hue locus until it intersects the constant brightness locus at B. The coordinates of A and B are thus found. The color difference between that of a given representative dye solution and that of a standard dye solution is obtained from the coordinates of A and B and the following formulae [8].
The above operation is repeated on two or more, preferably several, representative samples to determine the abovementioned color difference with respect to the standard dye for each sample.

(3) A customary dyeing test is performed on the standard dye and the same representative samples as used above. The respective differences between the colors of dyeings of each representative sample and the color of the dyeing of the standard dye are each measured in terms of hue difference and saturation or brightness difference.
(4) The relation between the color difference (from that of the standard dye) of dye solution and the color difference of dyeings is statistically determined in the form of a regression line (Fig. 11) or in other forms.
(5) The color difference between that of a solution of the standard dye and that of a solution of the sample dye is determined in the same manner as in (2).
(6) It is thus possible to predict the color difference between dyeings of sample dyes as compared with the dyeing of the standard dye in terms of hue difference and brightness difference from the color difference between that of the dye solution of the sample dye and that of the standard dye solution obtained in (5) by referring to the relation established in (4).

The invention is illustrated below with reference to Examples, in which all parts are by weight.

Example 1

Measurement of Color Difference of Representative Sample Solution

Color Index (C.I.) Disperse Blue 301 is separated into individual components by means of a high speed liquid chromatography under the. following conditions of separation. The dye solution for injection is prepared by dissolving 0.12 part of the dye in acetonitrile and making up to 100 parts with the same solvent.
Conditions for high speed liquid chromatographic separation:

Column: Lichrosorb RP₁₈ (Sumika Analytical Center Co.)
Mobile Phase: Liquid A: Water
Liquid B: Acetonitrile
Elution: Gradient method.

The concentration of liquid B is increased from the starting concentration of 60% to 70% after 20 minutes, then to 100% after subsequent 15 minutes.

Flow rate: 1 ml/minute.
Monitering wavelength: 592 nm.
Sample volume: 5 pl

The content of each component is determined by the method of peak area normalization and the ratio of each separated component to the main component is calculated (Table 1).
In the next step, each of the separated components is measured to determine its distribution of absorbance curve in the visible spectrum range by means of a rapid scanning spectrophotometer shown in Fig. 12. The absorbance distribution curve per unit of content is constructed by plotting the quotient obtained by dividing absorbance by the ratio of individual component to main component (hereinafter this quotient is referred to as absorbance coefficient). In Table 2 are shown absorbance coefficients (DnÀ) of each component thus obtained (wavelength interval is 10 nm).
Into 300 parts of water, is added 0.2 part of the aforementioned sample dye together with 10 parts of spun polyester yarn. The mixture is heated at 130°C under applied pressure for 60 minutes to effect dyeing. After dyeing, the yarn is washed with hot water, then subjected to reduction clearing and subsequent drying. In a customary manner, 1 part of the dyed yarn is extracted with 50 parts of chlorobenzene. Individual components contained in the extract are separated and quantitatively determined by liquid chromatography under the aforementioned conditions of separation to select the components fixed onto the yarn. In the liquid chromatogram shown in Fig. 3, the components No. 1, 2, 3 and 7 are unfixed components, so their dyeing affinities S_l, S₂, S₃ and 8₇, respectively, are assumed to be 0, whereas those of other components are assumed to be 1.0.
Separation and quantitative determination of individual components of the standard dye and two or more representative samples are carried out under the same conditions of separation as described above. Using the ratio, Pn (Table 3), of separated individual component to main component thus determined with respect to the standard dye and representative sample, the mixing calculation is carried out according to the aforementioned formulae [1]. The absorbances of mixtures with respect to the standard dye and the representative sample are as shown in Tables 4 and 5, respectively.
From the above values of absorbance and the aforementioned formulae [3], complementary tristimulus values QX, QY and QZ are calculated. The values obtained are

for the standard dye and

for the representative sample.
From the above tristimulus values and the aforementioned formulae [4], the complementary chromaticity coordinates xQ, yQ and the integrated optical density SQ are calculated. The values obtained are

for the standard dye and

for the representative sample.
A complementary chromaticity diagram as shown in Fig. 4 is constructed from the above results. In Fig. 4, 1 pertains to the standard dye and 2 to the representative sample.
By means of the formula [5] the distribution curve of absorbance of the. standard dye is transformed into the distribution curve of transmittance and the tristimulus values X, Y and Z are computed from the aforementioned formulae [6].

The coordinates are transformed by means of formulae [7] into a uniform color scale such as, for example, CIE 1976 (L^*a^*b^*) colorimetric system recommended by CIE.
In the a^*b^* chromaticity coordinates of this colorimetric system, four chromaticity points a^*(T), b^*(1); a^*(2), b^*(2); a^*(3), b^*(3); and a^*(4), b^*(4) are given when the chromaticity point a^*(0), b^*(0) representating a hue difference and a saturation or brightness difference undergoes independently a change of one unit.
Four sets of tristimulus values, X(1) . . . X(4), Y(1) . . . Y(4), and Z(1) . . . Z(4), corresponding to the above four chromaticity points are calculated by the reverse transformation of formulae [7].
Spectral transmittance curves Tλ which represent these tristimulus values are computed by the method of computer color matching calculation for transparent color or by other methods (Figs. 6 to 9).
The spectral transmittance curve Tλ is then transformed into the absorbance distribution curve by the reverse transformation of formulae [5]. From the curve and formulae [3] and [4], complementary chromaticity coordinates of the chromaticity points xQ(0) ... xQ(4), yQ(0) ... yQ(4) are calculated.
The differences between the complementary chromaticity coordinates of the standard dye and those of the four chromaticity points obtained above, that is, ΔxQ(1) . . . ΔxQ(4), ΔyQ(1) . . . AyQ(4), are calculated and the relating formulae are derived.
In Fig. 10, 0 is complementary chromaticity coodinates of the standard dye and 1, 2, 3 and 4 represent the complementary chromaticity coordinates corresponding to a hue difference and'brightness difference of 1.0.
In Fig. 10, a straight line is drawn through chromaticity point 0 at a mean inclination of the straight line connecting chromaticity points 0 and 1 and the straight line connecting chromaticity points 0 and 2 (the straight line drawn above can be substituted by the straight line connecting the chromaticity points 0 and 2; hereinafter referred to as constant brightness locus). A straight line parallel to the above drawn straight line is drawn through the complementary chromaticity point of the representative sample until it intersects at A a straight line drawn through chromaticity point 0 at a mean inclination of the straight line connecting chromaticity points 0 and 3 and the straight line connecting chromaticity points 0 and 4 (the above drawn straight line can be substituted by the straight line connecting chromaticity points 0 and 3; hereinafter referred to as constant hue locus). The coordinates of the intersection A are found to be

Similarly, a straight line parallel to the constant hue locus is drawn through the complementary chromaticity coordinates until it intersects the constant brightness locus at B, the coordinates of which are found to be

Using these values the required color difference between respective solutions of a representative and a standard dye solution is calculated in terms of hue difference of solution and brightness difference of solution in the following way:

Hue difference
Brightness difference

The above operation is repeated by selecting several representative samples each different from one another in their proportions of coloring matter components.

Measurement of Color Difference of Dyeings on Representative Samples

Into 300 parts of water, are added 10 parts of spun polyester yarn and 0.2 part of the standard dye or each of the same representative samples as used above. The mixture is heated at 130°C under applied pressure for 60 minutes to effect dyeing. After dyeing, the dyed yarn is washed with hot water and subjected to reduction clearing and subsequent drying. The color difference of dyeings of the representative sample against the standard dye is determined in terms of hue difference and brightness difference.

Determination of Relationship Between Color Difference of Dyeings and Color Difference of Dye Solution With Respect to Representative Sample

Using the data of color difference of dyeings and the color difference of solution obtained above, regression analysis is performed to determine the relationship in the form of regression line between the color difference of dye solution and the color difference of dyeings with respect to representative samples (Fig. 11).

Measurement of Color Difference of Solution of Sample Dye

In a manner similar to that described previously, the color difference of solution of the sample dye is measured in terms of hue difference and brightness difference against the standard dye.

Prediction of Color Difference of Dyeings with Respect to Sample Dye

Using the color difference of solution of the sample dye obtained above, the predicted color difference of dyeings is obtained from the regression line. In Table 6 are shown both the predicted color difference thus obtained and the color difference obtained by actual dyeing with the sample dye.
The values of predicted color difference of dyeings obtained on another sample dye Nos. (1-2)-(1-8) are shown in Table 7 together with the results of dyeing in side-by-side arrangement.
As is seen from the above experimental results, the predicted values of color difference of dyeings obtained by the above method (predicted color difference of dyeings) show satisfactory agreement with the values obtained by actual dyeing (result of dyeing).

Example 2

Measurement of Color Difference of Solution of Representative Dye

Measurements are performed with respect to C.I. Disperse Blue 79, a disperse dye difficultly soluble or insoluble in water. The absorbance coefficient of individual component contained in the dye (Table 8) and the ratio of separated component to main component of the standard dye and the representative sample are measured as in Example 1 (Table 9).
The absorbance distribution curve for each component is obtained by multiplying the absorbance coefficient of each component by the ratio of corresponding component to main component, except that in the case of components 1 and 2 which do not dye, the absorbance coefficient is multiplied by the dyeing coefficient which is zero in such a case. The complementary chromaticity coordinates, xQ, yQ and the integrated optical density, SQ, corresponding to each component are calculated from the above values and the formulae [3] and [4]. The coordinates xQ, yQ and the integrated optical density SQ of each component of the standard dye and the representative dye are found to be as shown in Tables 10 and 11, respectively.
The complementary coordinates xQ, yO and the integrated optical density SQ of the standard dye are obtained by.the color mixing calculation on the complementary chromaticity coordinates according to the formulae [2] in the following way using the values obtained above for the components.
The mixing of complementary chromaticity coordinates of LC No. 3 and those of LC No. 6 gives the following formulae:

The mixing of the above mixed coordinates with the complementary chromaticity coordinates of LC No. 7 leads to the following formulae:
In the above formulae each numeral in parentheses is the corresponding LC No. and the mark ^* means the mixed complementary chromaticity coordinates. In a similar manner, the resultant mixed coordinates are mixed successively with the complementary chromaticity coordinates of LC Nos. 11, 12 and 15 to obtain the complementary chromaticity coordinates of the standard dye:
The complementary chromaticity coordinates and the integrated optical density of the representative sample are similarly obtained:
On plotting the above values, there is obtained a complementary chromaticity diagram shown in Fig. 13, wherein 1 refers to the standard dye and 2 to the representative sample.
By means of the formula [5] the absorbance distribution curve of the standard dye of the same family is transformed into the transmittance distribution curve and the tristimulus values X, Y, Z are computed from the formula [6].

The coordinates are transformed by means of formulas [7] into a uniform color scale such as, for example, CIE 1976 (L^*a^*b^*) colorimetric system recommended by CIE.
In the a^*b^* chromaticity coordinates of this colorimetric system, four chromaticity points a^*(1), b^*(1); a^*(2), b^*(2); a^*(3), b^*(3); and a^*(4), b^*(4) are given when the chromaticity point a^*(0), b^*(O) representing a hue difference and a saturation or brightness difference undergoes independently a change of one unit.
Then, 4 sets of tristimulus values, X(1) ... X(4), Y(1) ... Y(4), and Z(1) ... Z(4), corresponding to the above four chromaticity points are calculated by the reverse transformation of formulae [7].
Spectral transmittance curves Tλ which represent these tristimulus values are computed by the method of computer color matching calculation for transparent color or by other methods. The spectral transmittance curve Tλ is then transformed into the absorbance distribution curve by the reverse transformation of formulae [5]. From the resulting curve and formulae [3] and [4], complementary chromaticity coordinates of each chromaticity point xQ(0) ... xQ(4), yQ(0) . . . yQ(4) are calculated.
The differences between the complementary chromaticity coordinates of the standard dye and those of the four chromaticity points obtained above, that is, ΔxQ(1) ... ΔxQ(4), ΔyQ(1) ... ΔyQ(4), are calculated and the relating formulae are derived.
In a manner similar to that described in Example 1, the constant hue locus and the constant brightness locus are determined and a straight line parallel to the latter line is drawn through the complementary chromaticity coordinates of the representative sample to intersect the constant hue locus at A, the coordinates of which are then determined

Another straight line parallel to the constant hue locus is drawn also through the complementary chromaticity coordinates of the representative sample to intersect the constant brightness locus at B and the coordinates of B are then determined.

The color difference of a representative dye solution in terms of hue difference and brightness difference as compared with the standard dye solution is determined from these values.
The above operation is repeated by selecting several representative samples each different from one another in their proportions of coloring matter components.

Measurement of Color Difference of Dyeings on Representative Samples

Into 300 parts of water, are added 10 parts of spun polyester yarn and 0.2 part of the standard dye or each of the same representative samples as used above. The mixture is heated at 130°C under applied pressure for 60 minutes to effect dyeing. After dyeing, the dyed yarn is washed with hot water and subjected to reduction clearing and subsequent drying. The color difference of dyeings of each representative sample against the standard dye is determined in terms of hue difference and brightness difference.

Using the data of color difference of dyeings and the color difference of solution obtained above, regression analysis is performed to determine the relationship in the form of regression line between the color difference of dye solution and the color difference of dyeings. Regression lines represented by the following equations are obtained:

Measurement of Color Difference of Solution of Sample Dye

Prediction of Color Difference of Dyeings with Respect to Sample Dye

The predicted color difference of dyeings of the sample dye is obtained from the equations obtained above and the measured color difference of solution of the sample dye. In Table 12 are shown both the predicted color difference thus obtained and the color difference obtained by actual dyeing with the sample dye.
The values of predicted color difference of dyeings obtained on other samples Nos. 2-2 to 2-8 are shown in Table 13 together with the results of dyeing in side-by-side arrangement.
As is seen from the above experimental results the predicted values of color difference of dyeings obtained by the above method (predicted color difference of dyeings) show satisfactory agreement with the values obtained by actual dyeing (result of dyeing).

. Example 3

Measurements are performed with respect to C.I. Disperse Blue 139, a disperse dye having low solubility or insoluble in water.
The absorbance distribution curve in the visible spectrum range is determined by absorption spectrophotometry on the solution prepared by dissolving 0.005 part of a standard dye or a representative sample in 80% acetonitrile and making up to 100 parts with 80% acetonitrile.
From the curve obtained above and the formulas [3] and [4], complementary chromaticity coordinates xQ, yQ are calculated. For the standard dye, they are

and for the representative dye
As in Example 1 or 2, the absorbance distribution curve for the standard dye is transformed into the transmittance curve by means of formula [5] and tristimulus values X, Y and Z are obtained by means of formulae [6]. The tristimulus values are transformed by means of formulae [7] into a uniform color scale such as, for example, CIE 1976 (L^*a^*b^*) colorimetric system recommended by CIE.
In the a^*b^* chromaticity coordinates of the above CIE colorimetric system, four chromaticity points are given when the chromaticity point representing the hue difference and the saturation or brightness difference undergoes independently a change of one unit. Then, 4 sets of tristimulus values corresponding to said four chromaticity points are calculated by the reverse transformation of formulae [7]. Spectral transmittance curves which give the above tristimulus values are computed by the method of computer color matching calculation for transparent color or by other methods. The spectral transmittance curve is then transformed into the absorbance distribution curve by the reverse transformation of formula [5]. From the resulting curve and formulae [3] and [4], complementary chromaticity coordinates of each chromaticity point are calculated. The difference between the complementary chromaticity coordinates of the standard dye and those of the four chromaticity points obtained above, that is, ΔxQ(1) ... ΔxQ(4), ΔyQ(1) ... AyQ(4), are calculated and the relating formulae are derived.
In a manner similar to that described in Example 1 or 2, the coordinates of the intersection A on the constant hue locus are determined.

Likewise, the coordinates of the intersection B on the constant brightness tocus are determined.

The color difference of dye solution is determined from the above values
The above sequence of operation is repeated on several representative samples each different from one another in their proportions of coloring matter components.
On the other hand, in a manner similar to that in Example 1 or 2, the color difference of dyeings of the representative sample against the standard dye is determined. Using the data of color difference of dyeings and the color difference of dye solution, regression analysis is performed to determine the relationship in the form of regression line between the color difference of dye solution and the color difference of dyeings. Regression lines represented by the following equations are obtained:
Using the equations, predicted color difference of dyeings of the sample dye is obtained from the color difference of solution of the sample dye determined in a similar manner to that described above. In Table _- 14 are shown both the predicted color difference of dyeings and the color difference obtained by actual dyeing with the sample dye.
The values of predicted color difference of dyeings obtained on other samples Nos. 3-2 to 3-8 are shown in Table 15 together with the results of dyeing in side-by-side arrangement.
As is seen from the above experimental results, the predicted values of color difference of dyeings obtained by the above method (predicted color difference of dyeings) show satisfactory agreement with the values obtained by actual dyeing (result of dyeing).

Example 4

Predicted color difference of dyeings is obtained in the same manner as in Example 1 or 2, except that the dye used is C.I. Reactive Red 111, a water-soluble dye. The predicted color difference is compared with the result of actual dyeing as shown in Table 16.
As is seen from the experimental results, the predicted values of dyeing result (predicted color difference of dyeings) obtained according to this invention show satisfactory agreement with the result of actual dyeings (result of dyeing).

Claims

1. A method for measuring the color difference between a sample dye and a standard dye by testing the color properties of both dyes, which comprises the steps of isolating from dyes of the same family each of the coloring matter components having a dyeing affinity and having the possibility of existing in the dye; measuring the spectral absorbance or spectral transmittance of each component in solution form to obtain data 1 to be filed; selecting two or more dyes having such compositions that the proportions of the coloring matter components are different to some degrees from those of the sample dye, then quantitatively analyzing said prepared or selected dyes and a standard dye for their coloring matter components; calculating the spectral absorbance or spectral transmittance of each of said prepared or selected dyes and said standard dye by the method of color mixing calculation in accordance with the composition of each dye using the results of above quantitative analysis and the filed data 1 of each coloring matter component; calculating the color difference in solution between each of said selected dyes and the standard dye; dyeing with said selected dyes and the standard dye to determine the color difference by colorimetry; determining statistically the numerical relationship between the color difference of dye solution and the color difference of dyeings to acquire data 2; after collecting the foregoing data 1 and 2, analyzing quantitatively the sample dye for the coloring matter components; calculating the tristimulus values of the solution of sample dye from the results of said quantitative analysis and data 1 of each coloring matter component; calculating the color difference in solution from the calculated tristimulus values and the tristimulus values of the standard dye (which are determined previously or simultaneously); and converting the calculated color difference of solution into the color difference of dyeings by means of data 2.

2. A method according to Claim 1, wherein using a standard dye and two or more representative samples, the relationship between the color difference relative to the standard dye of solution and the color difference relative to the standard dye of dyeings is determined for said representative samples according to the following procedure

(1) each of the components contained in the dyes of the same family is separated and collected separately by chromatography; for each separated component the spectral absorbance curve is measured and from each curve a spectral absorbance curve per unit of each component content is derived;

(2-a) the calculation for color mixing is performed by using the absorbance curve per unit of content obtained in (1) and the results of quantitative analysis of the separated components with respect to the standard dye and representative samples of the same family as that of the standard dye; a color coordinate system representing the value of color property unaffected by the variation in concentration of the solution, such as the values of complementary chromaticity coordinates, is selected; complementary tristimulus values QX, QY, QZ are calculated for the standard dye and the sample dye by the same method of calculating the tristimulus values using the absorbance in place of the transmittance; from the calculated complementary tristimulus values, there are obtained complementary chromaticity coordinates xQ, yQ and the integrated optical density SQ; which is the sum of QX, QY, QZ;

(2-b) a dye is selected from the dyes of the same family and tristimulus values X, Y, Z are calculated from the spectral transmittance curve of the dye; these values are then transformed into a suitable uniform color scale; in the coordinate diagram of this color system, four sets of tristimulus values given by points that undergo a change of one unit independently in hue difference and in saturation or brightness difference from the point of the dye are calculated and the corresponding transmittance curve is derived by color mixing calculation; the transmittance curve is transformed into the distribution curve of absorbance to obtain the complementary chromaticity coordinates of each chromaticity point; from the difference between these coordinates and the complementary chromaticity coordinates of the dye selected above, the relation of the hue difference and saturation or brightness difference to the difference in complementary chromaticity coordinates in the uniform color scale is established; by referring to the established relationship, the color difference of representative sample relative to the standard dye is calculated in terms of hue difference and saturation or brightness difference; the foregoing operation is repeated on two or more, representative dyes different from one another in proportions of coloring matter components;

(3) dyeings are prepared from the standard dye and the representative samples of which the color difference of solution have been determined above; from the dyeings, there is obtained the color difference, of the representative dye relative to the standard dye;

(4) the relationship between the color difference of dye solution determined in (2) and the color difference of dyeings determined in (3) is found in terms of hue difference and saturation or brightness difference;

(5) using the standard and the sample dye, the color difference of solution of the sample dye relative to the standard dye is calculated in terms of hue difference and saturation or brightness difference, as described in (2);

(6) the color difference of dyeings of the sample dye is predicted from the color difference of solution of the sample dye obtained in (5) and the relationship established in (4).

3. A method according to Claim 2, wherein high speed liquid chromatography is used as a means for separating individual components contained in a dye.

4. A method according to Claim 2, wherein the absorbance curve per unit of each components is corrected in step (1) using a weighting factor pertaining to dyeing affinity.

5. A method according to Claim 2, wherein the absorbance curve per unit of each component is corrected in step (2a) using a weighting factor pertaining to dyeing affinity.